Method of blending fuel

ABSTRACT

The present invention relates to a method of blending a multi-component blended fuel. The method comprises selecting as a starting reference a known multi-component blended fuel (e.g. a blend of gasoline and ethanol) which is in use by an internal combustion engine which operates SI or HCCI combustion. The method comprises blending an alternative fuel which can be used by the same engine without modification of the engine, including without modifying the operating regime employed by its engine management system. The alternative fuel is a blend comprising all of the components of the known fuel and an additional fuel component (e.g. methanol). The blend components are blended in proportions which give to the alternative fuel: a stoichiometric air-fuel ratio by mass or by volume substantially equal to that of the known blended fuel; and/or a lower heating valve (e.g. volumetric or gravimetric) substantially equal to that of the known blended fuel; and/or produces a response from an ethanol sensor substantially equal to that of the known blended fuel.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a U.S. national phase of PCT/GB2010/000793, with an international filing date of 21 Apr. 2010, which is incorporated by reference in its entirety herein, claiming priority from United Kingdom Application No. 0906860.2, filed 21 Apr. 2009.

BACKGROUND

The present invention relates to fuels, their use in internal combustion engines in vehicles and their production. Specifically, the present invention relates to blended fuels, particularly including methanol with stoichiometric air-fuel ratios similar to that of E85.

It is known to produce fuels by blending ethanol and gasoline in various proportions. Such fuels can be used in unmodified gasoline internal combustion engines, e.g. in automobiles, or gasoline internal combustion engines with only minor modifications.

Ethanol-based fuels are usually denoted by the letter “E” followed by the proportion by volume of ethanol, expressed as a percentage. For example, a common blend is E85; a mixture of 85% ethanol by volume with 15% gasoline by volume. These two-component blended fuels may contain other additives, but these additives are not fuel components, do not have significant volume and do not significantly affect the proportions of the major fuel components, ethanol and gasoline, which together can be considered the only significant fuel components. In the following description the term component(s) refers exclusively to a fuel component(s).

Gasoline fuel (sometimes called petrol) is itself a blend of hydrocarbons, typically aliphatic hydrocarbons obtained by fractional distillation of petroleum, enhanced with iso-octane or the aromatic hydrocarbons toluene and benzene. The term gasoline is used throughout this specification to refer to fuel suitable for use in an internal combustion engine running spark-injection (“SI”) combustion or Homogenous Charge Ignition Combustion (“HCCI”) which is composed of hydrocarbons (typically between 4 and 12 carbon atoms per molecule) and is substantially free of oxygenated components, e.g. alcohols and ethanols, (less than 5% oxygen content) and which has a stoichiometric Air-fuel ratio in the range 14:1 to 15:1. Preferably the fuel has a Research Octane Number (RON) of 86 to 105. The term gasoline is used to include fuels such as those defined by British Standard BS/EN228 and/or American Standard ASTM-D-4814.

In the UK it is now possible to purchase for use in internal combustion engines of motor vehicles E5 (5% ethanol, 95% gasoline). The use of E10 (10% ethanol, 90% gasoline) for motor vehicle internal combustion engines is increasing in the US.

It is now becoming popular to manufacture internal combustion engines which are specifically configured to run on a fuel blend of gasoline and ethanol. For example, in Brazil, all gasoline internal combustion engines (e.g. which run using the Otto cycle) are manufactured to run on blended fuels in the range E20 to E25.

The highest proportion of ethanol generally used for Otto-cycle internal combustion engines of vehicles is 85% by volume (E85), although it is known exceptionally to use 100% ethanol (E100).

The use of ethanol-based blended fuels is more environmentally friendly than simply using more gasoline, since the ethanol is typically produced from biomass. Furthermore, the use of ethanol reduces a country's dependence upon imports of foreign petroleum. However, the supply of ethanol from biomass is limited.

It is therefore advantageous to find fuel blends which can extend use renewable components of the fuel blends.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided a method as claimed in claim 1.

According to a second aspect of the present invention there is provided a blended fuel as claimed in claim 17.

According to a third aspect of the present invention there is provided a blended fuel as claimed in claim 18.

According to a fourth aspect of the present invention there is provided a blended fuel as claimed in claim 19.

According to a fifth aspect of the present invention there is provided a method as claimed in claim 20.

According to a sixth aspect of the present invention there is provided a method as claimed in claim 21.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 shows a graph showing the relative proportions of ethanol, gasoline and methanol in a blended fuel equivalent to E85; and

FIG. 2 shows a graph showing the relative proportions of methanol, gasoline and ethanol in a blended fuel equivalent to M85.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of three-component blended fuels in accordance with the invention can have the same properties as known two-component blended fuels, to thereby provide good performance in internal combustion engines of motor vehicles that have been designed to run on known two-component blended fuels. Importantly they can be used by existing internal combustion engine with no structural modifications of such engines, and preferably without any need for the engine management system to run a different operating regime for the new fuels (i.e. there is no need to ass to the memory of the engine management system new operating regime maps for the new fuels).

In order for a fuel to be compatible with an existing design of motor vehicle internal combustion engine (i.e., to offer significantly the same behaviour as the fuel on which the engine has been configured to run), the most preferable property of the fuel to be the same as the fuel on which the engine was designed to run, is the stoichiometric air-fuel ratio. This is the ratio (conventionally, and hereinafter, represented as a ratio by mass) of air to fuel which will theoretically provide complete combustion of the fuel.

Alternatively, since internal combustion engines that are configured to run on alcohol-based fuels comprise an alcohol sensor for determining the ratio of alcohol to gasoline in the fuel it may be advantageous to provide a blended fuel that provides substantially the same response when measured by an alcohol sensor as the fuel on which the engine was designed to run. Such a response may be, for example, that the resistance across the sensor changes as a result of varying proportions of ethanol in the fuel. Preferably, the resistance will be the same for the three-component blended fuel as for the fuel on which the engine was designed to run. Typically, the engine management system will use this measurement to determine the volume of fuel to be delivered in each engine cycle.

As a further alternative, it may be advantageous to provide a blended fuel that provides the same lower heating value (e.g. volumetric or gravimetric) as the fuel on which the engine was designed to run.

According to a first embodiment of the invention there is provided a blended-fuel having an equivalent stoichiometric air-fuel ratio (AFR) as E85.

The stoichiometric AFR of ethanol is approximately 8.96:1. The stoichiometric AFR of gasoline is approximately 14.53:1. A blend of 85% ethanol with 15% gasoline has a stoichiometric AFR of 9.74:1.

Any ethanol-gasoline blended fuel will have a stoichiometric AFR lying between the upper and lower bound defined by the stoichiometric AFRs of gasoline and ethanol, respectively.

If a larger proportion of gasoline is used, then the stoichiometric AFR will increase. This is because gasoline has a larger stoichiometric AFR than ethanol. Clearly, the maximum stoichiometric AFR achievable with these two components is 14.53:1, which is achieved by 0% ethanol and 100% gasoline.

In order to provide a fuel having a stoichiometric air-fuel ratio that is the same as E85, whilst reducing the proportion of ethanol, it is necessary to add a fuel component having a lower stoichiometric AFR than E85.

In the first embodiment, methanol is blended with ethanol and gasoline to provide a fuel having 65% ethanol by volume and a stoichiometric AFR of 9.74:1 (i.e., the same stoichiometric AFR as E85).

The stoichiometric AFR of methanol is approximately 6.44:1.

The blend of 65% ethanol with gasoline and methanol that provides a stoichiometric AFR of 9.74:1 is approximately: 65% ethanol; 21.5% gasoline; and 13.5% methanol.

Advantageously, a fuel with less ethanol can therefore be produced without significantly increasing the reliance upon fossil fuels. This is because methanol can be synthesised from hydrogen and atmospheric carbon dioxide and/or carbon monoxide or made from wood waste (although less advantageously, the methanol could be made from coal or natural gas).

A blended fuel with increased methanol will offer better performance than E85 when starting the internal combustion engine in low temperature conditions. Typically, where an E85 blend is offered in summer conditions, a winter blend of E70 is offered in colder conditions. A blend with methanol could remove the need for providing a more gasoline rich blend of ethanol-based fuel (i.e. the winter-grade E70 blend) in cold conditions.

According to a second embodiment of the invention there is provided a method of producing a blended fuel having an equivalent stoichiometric air-fuel ratio (AFR) as E85.

For the methodology described below the following values are used:

Fuel Stoichiometric Gravimetric Density Molecular Component AFR (:1) LHV (MJ/kg) (kg/l) Mass (—) Ethanol 8.5982 26.8 0.7892 46 Gasoline 14.5298 42.7 0.7359 114.56 Methanol 6.4375 19.9 0.7913 32 LHV stands for Lower Heating Valve (also known as calorific value) and is defined as the amount of heat released by combusting a specified quantity (mass or volume) in controlled temperature conditions.

FIG. 1 shows a graph of proportion by volume of ethanol against corresponding proportions of gasoline (denoted by triangles) and methanol (denoted by circles). (That is, the X-axis represents the proportion of ethanol and the Y-axis represents the proportion of both gasoline and methanol).

The lines are provided by the following equations:

V _(gas)=42.641−0.3255×V _(eth)  (Equation 1)

V _(meth)=57.359−0.6745×V _(eth)  (Equation 2)

where V_(eth), V_(gas) and V_(meth) are, respectively, the proportions of ethanol, gasoline, and methanol by volume that provide the stoichiometric AFR of E85.

The method of the second embodiment comprises blending a desired proportion of ethanol with a first proportion of gasoline and a second proportion of methanol such that the resulting blended fuel has the same stoichiometric AFR as E85.

For example, if a fuel is desired with only 50% ethanol, the blend of ethanol, gasoline and methanol that provides the same stoichiometric AFR as E85 would be approximately: 50% ethanol; 26.4% gasoline; and 23.6% methanol.

The desired proportion is entered as V_(eth) into Equation 1 to determine the first proportion, and into Equation 2 to determine the second proportion.

The above disclosed blends of ethanol, gasoline and methanol would be usable in internal combustion engines that have been configured to run on E85. Advantageously, the use of methanol as a third fuel component does not adversely effect the operation of the engine, since the variation in ethanol sensor measurements to fuel also including methanol is only small.

In various embodiments, the amount of ethanol by volume in the fuel would be in the range of 40% to 85%. Over this range, the variation in output level from a typical ethanol sensor will vary by no more than 3.5%

Another advantageous feature of blending methanol with ethanol and gasoline is that the volumetric lower heating value (LHV) of the blend remains substantially unchanged over the range of 0% to 85% ethanol by volume as compared with E85. This change is less than 1%, which is smaller than the variation caused by different sources of gasoline. As such, it is not necessary to modify the operating regime employed by or the parameters of the engine management system to command the fuel injector to deliver a different amount of fuel. This result has also been found to be the case for other standard vehicle engine alcohol sensors when other three-component blended fuels replace two-component blended fuels (e.g. replacing M85 with a blend of ethanol, methanol and gasoline).

However, if desired, the engine management system can be modified to compensate for the new fuel by using the following equation:

Volumetric LHV=22.496+(0.0025×V _(eth))  (Equation 3)

where Volumetric LHV is measured in MJ/l, and V_(eth) is the proportion of ethanol by volume.

Equation 3 is derived from a line of best-fit through empirical data obtained from measuring the volumetric lower heating value of a number of blended fuels having proportions of ethanol, gasoline, and methanol, related by equations 1 and 2.

Since, as disclosed above, the variation of LHV is so small, any modification of the volume of fuel to be delivered will lie within the operating range of the fuel injector.

In the above embodiments a fuel and a method of producing the same have been disclosed for a fuel that has substantially the same stoichiometric AFR as E85.

However, it may be desirable to provide a blended fuel with low ethanol content that has substantially the same stoichiometric AFR as a different ethanol-gasoline based fuel (i.e. a fuel having substantially only ethanol and gasoline as components), such as E65 or E50.

As will be appreciated by the skilled person, since methanol has a lower stoichiometric AFR than either ethanol or gasoline (and therefore also a lower stoichiometric AFR than any ethanol-gasoline blend), any ethanol-gasoline based fuel having a significant proportion of ethanol may be replaced by one having less ethanol but the same stoichiometric AFR, by blending different amounts of ethanol, gasoline and methanol.

Moreover, the skilled person will appreciate that the above disclosed concept is not limited to methanol and that any component having a lower stoichiometric AFR than the ethanol-based fuel to be replaced may be blended with ethanol and gasoline to thereby provide a blended fuel with a suitable stoichiometric AFR. Preferably, such a component would belong to at least one of the following groups: pure hydrocarbons; alcohols; ethers; or furans.

Similarly, gasoline may be replaced with any component having a higher stoichiometric AFR than the ethanol-based fuel to be replaced.

Although the above has been described as providing the same stoichiometric AFR as ethanol-based fuel blends, blended fuels may be developed with any first, second and third components to provide a blended fuel having the same stoichiometric AFR as any fuel to be replaced, provided that two of the components have a higher and lower stoichiometric AFR, respectively, than the fuel to be replaced (i.e., the target stoichiometric AFR).

In other words, for vehicles designed to run on a two-component blended fuel having a first component and a second component, a three-component fuel can be provided having the first component and the second component and a third component. The three-component fuel can have a smaller proportion of the first component than the two-component fuel whilst having the same stoichiometric AFR, provided that the second and third components have a stoichiometric AFR greater than and lower than the stoichiometric AFR of the two-component blended fuel (or vice versa).

According to a third embodiment of the present invention, there is provided a method of producing a three-component blended fuel for an internal combustion engine that has been configured to run on a two-component blended fuel formed from methanol and gasoline. Specifically, in this embodiment, the two-component fuel is M85. However, the skilled person will appreciate that the following describes a technique which may be applied to any methanol-gasoline blend (and furthermore, as described above, any two-component blended fuel).

As with the second embodiment, the three-component fuel is chosen to have the same stoichiometric AFR as the two-component fuel. However, it is possible to produce a three-component blended fuel in which a different property (such as volumetric LHV or the signal produced by an ethanol or methanol sensor) of the fuel is the same as for the two-component blended fuels.

FIG. 2 shows a graph of proportion by volume of gasoline against corresponding proportions of methanol (denoted by triangles) and ethanol (denoted by circles). (That is, the X-axis represents the proportion of gasoline and the Y-axis represents the proportion of methanol or ethanol).

The lines are provided by the following equations:

V _(meth)=54.687±2.026×V _(gas)  (Equation 4)

V _(eth)=45.313−3.026×V _(gas)  (Equation 5)

where V_(eth), V_(gas) and V_(meth) are, respectively, the proportions of ethanol, gasoline, and methanol by volume that provide the stoichiometric AFR of M85.

The method of the third embodiment comprises blending a desired proportion of gasoline with a first proportion of methanol and a second proportion of ethanol such that the resulting blended fuel has the same stoichiometric AFR as M85.

The desired proportion is entered as V_(gas) into Equation 4 to determine the first proportion, and into Equation 5 to determine the second proportion.

Accordingly, the proportion of gasoline can be reduced from the level present in M85 (i.e., 15%) by the addition of an ethanol component, whilst maintaining a constant stoichiometric AFR. This is because ethanol has a lower stoichiometric AFR than gasoline and a higher stoichiometric AFR than methanol.

These equations can be rewritten as:

V _(gas)=14.976−0.3305×V _(eth)  (Equation 6)

V _(meth)=85.024−0.6695×V _(eth)  (Equation 7)

to thereby provide the appropriate proportions of gasoline and methanol for a desired proportion of ethanol.

The above disclosed blends of ethanol, gasoline and methanol would be usable in internal combustion engines that have been configured to run on M85.

Although the disclosed fuel blends have been described as providing the same stoichiometric AFR by mass (this is the most preferable property of the blended fuel to control) as the fuel to be replaced, it is also possible to provide a fuel blend having a different equivalent parameter. For example, the fuel blend may produce the same reading on an ethanol sensor as the fuel to be replaced. Alternatively, the fuel blend may have the same LHV (volumetric or gravimetric) as the fuel to be replaced. Also, it may be desirable to match the three-component blended fuels stoichiometric AFR by volume with that of the fuel being replaced.

Although the above embodiments describe a method of producing a blended fuel having three components, the invention is applicable to a fuel having more than three components and a desired value of stoichiometric AFR or another property. The existing fuel might, for instance, be a three component fuel, and the new comparable fuel produced by the method a four component fuel.

Thus the invention can provide starting with an existing three component fuel (e.g. gasoline, ethanol and methanol) and it is possible to use the above methods to obtain a blended fuel with more than three components because collectively, the first component and the additional components in excess of three can be thought of as a single component. 

1. A method of producing a first multi-component blended fuel having at least three fuel components, comprising: selecting a second known multi-component blended fuel having at least one fewer fuel component than the first multi-component blended fuel, the second known multi-component blended fuel being in use by an existing design of SI and/or HCCI internal combustion engine; producing the first multi-component blended fuel by blending together fuel components also found in the known multi-component fuel along with an additional fuel arrangement, wherein: at least one of the fuel components common to both the first multi-component blended fuel and the known multi-component blended fuel has a stoichiometric air-fuel ratio by mass or by volume higher than the stoichiometric air-fuel ratio by mass or by volume of the second known multi-component blended fuel; and/or has a lower heating value higher than the lower heating value of the second known multi-component blended fuel; and/or produces from an ethanol sensor of the engine a response smaller than the response provided by the second known multi-component blended fuel; and the additional fuel component: has a stoichiometric air-fuel ratio by mass or by volume lower than the air-fuel ratio by mass or by volume of the second known multi-component blended fuel; and/or has a lower heating value lower than the blended lower heating value of the second known multi-component blended fuel; and/or produces from the ethanol sensor of the engine a response larger than the response produced by the second known multi-component blended fuel; and the proportions of the said at least one fuel component and the additional fuel component in the first multi-component blended fuel are selected so that: the stoichiometric air-fuel ratio by mass or volume of the first multi-component blended fuel is substantially equal to that of the second known multi-component blended fuel; and/or the lower heating value of the first multi-component fuel is substantially equal to that of the second known multi-component blended fuel; and/or the first multi-component blended fuel produces from the ethanol sensor a response substantially equal to that of the second known multi-component blended fuel.
 2. A method as claimed in claim 1 wherein: the first multi-component blended fuel is a three-component blended fuel having substantially only a first component, a second component, and a third component; the second known multi-component blended fuel is a two-component fuel used by an existing design of internal combustion engine, the two-component blended fuel having substantially only the first component and the second component; and the first three-component blended fuel is produced with a smaller proportion of the first component than the second known two-component blended fuel, by: blending a first volume of the first component with: a second volume of the second component which is the fuel component having a higher stoichiometric air-fuel ratio by mass than the two-component blended fuel; and a third volume of the third component which is the additional fuel component having a lower stoichiometric air-fuel ratio by mass than the two-component blended fuel; and by calculating the second and third volumes such that the stoichiometric air-fuel ratio by mass of the first three-component blended fuel is substantially equal to that of the second known two-component blended fuel.
 3. A method as claimed in claim 1 wherein: the first multi-component blended fuel is a three-component blended fuel having substantially only a first component a second component and a third component; the second known multi-component blended fuel is a two-component fuel used by an existing design of internal combustion engine, the two-component blended fuel having substantially only the first component and the second component; and the first three-component blended fuel is produced with a smaller proportion of the first component than the two-component blended fuel, by: blending a first volume of the first component with: a second volume of the second component, which is the additional fuel component having a greater lower heating value than the two-component blended fuel; and a third volume of the third component, which is the additional having a lesser lower heating value than the two-component blended fuel; and by calculating the second and third volumes such that the lower heating value of the first three-component blended fuel is substantially equal to that of the second known two-component blended fuel.
 4. A method as claimed in claim 1, wherein: the first multi-component fuel is a three-component blended fuel having substantially only ethanol, a second component and a third component; the second known multi-component fuel is a two-component fuel used by an existing design of an internal combustion engine, the engine having an ethanol sensor used to control operation of the engine, the two-component blended fuel having substantially only ethanol and the second component, the first three-component blended fuel is produced with a smaller proportion of ethanol than the two-component blended fuel, by: blending a first volume of ethanol with: a second volume of the second component, which is the fuel component which produces a smaller response when sensed by the ethanol sensor than the two-component blended fuel; and a third volume of the third component, which is the additional fuel component which produces a larger response when sensed by an ethanol sensor than the two-component blended fuel; and by calculating the second and third volumes such that the response measured by an ethanol sensor to the first three-component blended fuel is substantially equal to that of the second known two-component blended fuel.
 5. A method as claimed in claim 1 wherein: the first multi-component fuel is a three-component blended fuel having substantially only a first component, a second component, and a third component; the second known multi-component fuel is a two-component fuel used by an existing design of internal combustion engine, the two-component blended fuel having substantially only the first component and the second component; the first three-component blended fuel is produced with a smaller proportion of the first component than the two-component blended fuel; by: blending a first volume of the first component with: a second volume of the second component, which is the at least one fuel component having a higher stoichiometric air-fuel ratio by volume than the two-component blended fuel; and a third volume of the third component, which is the additional fuel component having a lower stoichiometric air-fuel ratio by volume than the two-component blended fuel; and by calculating the second and third volumes such that the stoichiometric air-fuel ratio by volume of the first three-component blended fuel is substantially equal to that of the second known two-component blended fuel.
 6. A method of producing fuel as claimed in any preceding claim, wherein the second known multi-component blended fuel substantially comprises only ethanol and gasoline.
 7. A method of producing fuel as claimed in claim 6, wherein the known fuel substantially comprises 40% to 85% ethanol by volume and 60% to 15% gasoline by volume.
 8. A method of producing fuel as claimed in claim 7, wherein the known fuel substantially comprises 85% ethanol by volume and 15% gasoline by volume.
 9. A method of producing fuel as claimed in any preceding claim, wherein the at least one fuel component common to both the first multi-component fuel and the known multi-component fuel is gasoline.
 10. A method of producing fuel as claimed in any preceding claim, wherein the additional fuel component is an alcohol.
 11. A method of producing fuel as claimed in claim 10, wherein the additional fuel component is methanol.
 12. A method of producing fuel as claimed in any one of claims 1 to 4, wherein the known multi-component blended fuel substantially comprises only methanol and gasoline.
 13. A method of producing fuel as claimed in claim 12, wherein the known fuel substantially comprises 40% to 85% methanol by volume and 60% to 15% gasoline by volume.
 14. A method of producing fuel as claimed in claim 13, wherein the known fuel substantially comprises 85% methanol by volume and 15% gasoline by volume.
 15. A method of producing fuel as claimed in any one of claims 12 to 14, wherein the at least one fuel component common to both the first multi-component fuel and the known multi-component fuel is gasoline.
 16. A method of producing fuel as claimed in any one of claims 12 to 15, wherein the additional fuel component is an alcohol.
 17. A method of producing fuel as in claim 16, wherein the additional fuel component is ethanol.
 18. A blended fuel consisting essentially of ethanol, methanol and gasoline, wherein the proportion of each of ethanol, methanol and gasoline is selected so as to provide the same stoichiometric air-fuel ratio by mass, the same stoichiometric air-fuel ratio by volume, the same lower heating value and/or the same measurement on an ethanol fuel sensor, as a fuel consisting of 85% ethanol by volume and 15% gasoline by volume.
 19. A blended fuel comprising substantially only ethanol, gasoline, and a third component, for use in an internal combustion engine configured to run on E85, wherein: the blended fuel has a proportion of ethanol less than 85%, and the blended fuel comprises a first volume of ethanol blended with: a second volume of gasoline; and a third volume of the third component having a lower stoichiometric air-fuel ratio by mass than E85, and wherein: the second and third volumes are calculated such that the stoichiometric air-fuel ratio by mass of the blended fuel is substantially equal to that of E85.
 20. A method of producing a three-component blended fuel having substantially only a first component, a second component, and a third component, wherein the three-component blended fuel has a desired proportion of the first component and a stoichiometric AFR by mass equal to a desired value, the method comprising blending a first volume of the first component with: a second volume of the second component having a higher stoichiometric air-fuel ratio by mass than the desired value; and a third volume of the third component having a lower stoichiometric air-fuel ratio by mass than the desired value, to thereby produce the three-component blended fuel.
 21. A method of producing a blended fuel having a plurality of fuel components, comprising blending selected volumes of each fuel component to thereby produce the blended fuel, wherein: at least one fuel component has a higher stoichiometric air-fuel ratio by mass than the two-component blended fuel; at least one fuel component has a lower stoichiometric air-fuel ratio by mass than the two-component blended fuel; and the volumes of each component are selected such that the stoichiometric air-fuel ratio by mass of the blended fuel is substantially equal to a desired value of stoichiometric AFR.
 22. A method of producing a blended fuel as in claim 21, wherein the desired value of stoichiometric AFR is equal to the stoichiometric AFR of an existing fuel for use in an existing design of internal combustion engine.
 23. A method of producing a blended fuel as in claim 22, wherein the existing fuel is a two-component blended fuel.
 24. A method of producing a blended fuel as in claim 23, wherein the existing fuel is a blend of substantially only ethanol and gasoline.
 25. A method of producing a blended fuel as in claim 23, wherein the existing fuel is a blend of substantially only methanol and gasoline. 